Search

The $\beta$-decay of neutron-rich $^{129}$In into $^{129}$Sn was studied using the GRIFFIN spectrometer at the ISAC facility at TRIUMF. The study observed the half-lives of the ground state and each of the $\beta$-decaying isomers. The level scheme of $^{129}$Sn has been expanded with thirty-one new $\gamma$-ray transitions and nine new excited levels, leading to a re-evaluation of the $\beta$-branching ratios and level spin assignments. The observation of the $\beta$-decay of the (29/2$^{+}$) 1911-keV isomeric state in $^{129}$In is reported for the first time, with a branching ratio of 2.0(5)$\%$.

A high-precision branching ratio measurement for the superallowed Fermi $\beta^{+}$ emitter $^{62}$Ga was performed with the Gamma-Ray Infrastructure for Fundamental Investigations of Nuclei (GRIFFIN) spectrometer at the Isotope Separator and Accelerator (ISAC) radioactive ion beam facility at TRIUMF. The high efficiency of the GRIFFIN spectrometer allowed 63 $\gamma$-ray transitions, with intensities down to $\approx$1 part per million (ppm) per $^{62}$Ga $\beta^{+}$ decay, to be placed in the level scheme of the daughter nucleus $^{62}$Zn, establishing the superallowed $\beta$ branching ratio for $^{62}$Ga decay to be 99.8577$^{+0.0023}_{-0.0029}\%$, a factor of 4 more precise than the previous world average. For several cascades, $\gamma-\gamma$ angular correlation measurements were performed to assign spins and/or determine the mixing ratios of transitions. In particular, the spin of the 2.342 MeV excited state in the daughter nucleus $^{62}$Zn was definitively assigned as $J = 0$. This assignment resolves a discrepancy between previous measurements and has important implications for the isospin symmetry breaking correction, $\delta_{C1}$, in $^{62}$Ga superallowed Fermi $\beta$ decay.

Spectroscopy of doubly magic $^{132}_{50}$Sn$_{82}$ has been performed with the GRIFFIN spectrometer at TRIUMF-ISAC following the $\beta$ decay of $^{132}_{49}$In$_{83}$. The analysis has allowed for the placement of a total of 70 transitions and 29 excited states in $^{132}$Sn. Detailed spectroscopy has also been performed on $^{131}$Sb, resulting from the $\beta$ decay of $^{131}$Sn, produced from the $\beta$-delayed neutron decay of $^{132}$In. Measurement of $\gamma$-rays in both $^{131}$Sn and $^{131}$Sb has led to the determination of the $\beta$-delayed neutron emission probability, $P_{n}$, from $^{132}$In. This is the first time the $P_{n}$ has been measured for this nucleus using $\gamma$ spectroscopy, and the new value of 12.3(4)% is consistent with the most recent $\beta-n$ counting experiment. Additionally, $\gamma$-$\gamma$ angular correlations have been performed in $^{132}$Sn, supporting the spin assignments of several excited states. Novel ab initio calculations are presented which describe several of the excited states, and these are compared to the experimental spectrum.

Lifetimes of ${2}_{1}^{+}$ and ${4}_{1}^{+}$ states as well as some negative-parity and nonyrast states in $^{188--200}\mathrm{Hg}$ were measured using $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ electronic fast timing techniques with the ${\mathrm{LaBr}}_{3}(\mathrm{Ce})$ detector array of the GRIFFIN spectrometer. The excited states were populated in the $\ensuremath{\epsilon}/{\ensuremath{\beta}}^{+}$ decay of ${J}^{\ensuremath{\pi}}={7}^{+}/{2}^{\ensuremath{-}}\phantom{\rule{0.28em}{0ex}}^{188--200}\mathrm{Tl}$ produced at the TRIUMF-ISAC facility. The deduced $B(E2)$ values are compared to different interacting boson model predictions. The precision achieved in this paper over previous ones allows for a meaningful comparison with the different theoretical models of these transitional Hg isotopes, which confirms the onset of state mixing in $^{190}\mathrm{Hg}$.

The half-lives of three β-decaying states of 13149In82 have been measured with the GRIFFIN γ-ray spectrometer at the TRIUMF-ISAC facility to be T1/2(1/2−)=328(15)ms, T1/2(9/2+)=265(8)ms, and T1/2(21/2+)=323(55)ms, respectively. The first observation of γ rays following the βn decay of 131In into 130Sn is reported. The β-delayed neutron emission probability is determined to be P1n=12(7)% for the 21/2+ state and 2.3(3)% from the combined 1/2− and 9/2+ states of 13149In82 observed in this experiment. A significant expansion of the decay scheme of 131In, including 17 new excited states and 35 new γ-ray transitions in 13150Sn81 is also reported. This leads to large changes in the deduced β-branching ratios to some of the low-lying states of 131Sn compared to previous work with implications for the strength of the first-forbidden β transitions in the vicinity of doubly magic 13250Sn82. (Less)

A high-precision half-life measurement for the superallowed Fermi ${\ensuremath{\beta}}^{+}$ emitter $^{22}\mathrm{Mg}$ was performed at the TRIUMF-ISAC facility using a $4\ensuremath{\pi}$ proportional gas counter. The result of ${T}_{1/2}=3.87400\ifmmode\pm\else\textpm\fi{}0.00079$ s is a factor of 3 more precise than the previously adopted world average and resolves a discrepancy between the two previously published $^{22}\mathrm{Mg}$ half-life measurements.

The $\ensuremath{\beta}$-decay half-lives of $^{128--130}\mathrm{Cd}$ have been measured with the newly commissioned GRIFFIN $\ensuremath{\gamma}$-ray spectrometer at the TRIUMF-ISAC facility. The time structures of the most intense $\ensuremath{\gamma}$ rays emitted following the $\ensuremath{\beta}$ decay were used to determine the half-lives of $^{128}\mathrm{Cd}$ and $^{130}\mathrm{Cd}$ to be ${T}_{1/2}=246.2\phantom{\rule{0.16em}{0ex}}(21)$ ms and ${T}_{1/2}=126\phantom{\rule{0.16em}{0ex}}(4)$ ms, respectively. The half-lives of the $3/{2}^{+}$ and $11/{2}^{\ensuremath{-}}$ states of $^{129}\mathrm{Cd}$ were measured to be ${T}_{1/2}(3/{2}^{+})=157\phantom{\rule{0.16em}{0ex}}(8)$ ms and ${T}_{1/2}(11/{2}^{\ensuremath{-}})=147\phantom{\rule{0.16em}{0ex}}(3)$ ms. The half-lives of the Cd isotopes around the $N=82$ shell closure are an important ingredient in astrophysical simulations to derive the magnitude of the second $r$-process abundance peak in the $A\ensuremath{\sim}130$ region. Our new results are compared with recent literature values and theoretical calculations.

The half-life of the superallowed Fermi ${\ensuremath{\beta}}^{+}$ emitter $^{18}\mathrm{Ne}$ has been determined via two high-precision $\ensuremath{\beta}$ counting experiments at TRIUMF's Isotope Separator and Accelerator facility. Using two different $4\ensuremath{\pi}$ continuous-flow gas-proportional counters, two independent measurements were made, yielding a weighted average of ${T}_{1/2}=1.{66400}_{\ensuremath{-}0.00048}^{+0.00057}$ s, which is consistent with but approximately 2 times more precise than a previous high-precision measurement based on $\ensuremath{\gamma}$-ray counting. The present work achieves $\ifmmode\pm\else\textpm\fi{}0.034%$ precision for the $^{18}\mathrm{Ne}$ half-life and will enable the inclusion of $^{18}\mathrm{Ne}$ among the set of precisely measured superallowed Fermi $\ensuremath{\beta}$-decay $ft$ values once improved measurements are made for its $Q$ value and superallowed branching ratio. As a test of systematic uncertainties, the half-life of $^{23}\mathrm{Ne}$ was measured and the world average has been improved, by a factor of 1.7, to $37.148\ifmmode\pm\else\textpm\fi{}0.032$ s.